In a packet transmission system, there is known a method which is called a packet dispersion method which estimates a transmission rate of a link which is a bottleneck of a transmission rate from packet dispersion. Here, “packet dispersion” means a temporal spread of arrival intervals of a packet caused by a transmission delay. In patent document 1, a structure of a speed calculation system equipped with a function to estimate a speed of a link which will be a bottleneck by the packet dispersion method is disclosed.
An estimation method of a band of a link which is not a bottleneck is disclosed in patent document 2. The estimation method of a band disclosed in patent document 2 measures packet dispersion after, in a plurality of routes sharing a section to be measured, a packet group have passed the measured section. By this, the estimation method of a band disclosed in patent document 2 makes it possible to estimate a transmission rate of a measured section even when a band of the measured section is not a bottleneck in a route.